Controllable radiation lithographic apparatus and method

ABSTRACT

A lithographic arrangement allows for controlling radiation characteristics. An illumination system provides a beam of radiation from radiation provided by a radiation source. The radiation source includes an array of individually controllable elements, each individually controllable element being capable of emitting radiation. A support structure supports a patterning device. The patterning device imparts the radiation beam with a pattern. A projection system projects the patterned radiation beam onto a target portion of a substrate held by a substrate table. A radiation peak intensity detection apparatus detects a peak in the intensity of an emission spectrum of one or more of the individually controllable elements of the radiation source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) toProvisional Patent Application No. 61/088,909 filed Aug. 14, 2008, whichis incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a lithographic apparatus and devicemanufacturing method.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, which is alternatively referredto as a mask or a reticle, may be used to generate a circuit patterncorresponding to an individual layer of the IC, and this pattern can beimaged onto a target portion (e.g., including part of, one or severaldies) on a substrate (e.g., a silicon wafer) that has a layer ofradiation-sensitive material (resist). In general, a single substratewill contain a network of adjacent target portions that are successivelyexposed. Known lithographic apparatus include so-called steppers, inwhich each target portion is irradiated by exposing an entire patternonto the target portion in one go, and so-called scanners, in which eachtarget portion is irradiated by scanning the pattern through the beam ina given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti-parallel to this direction.

The use of an array of LEDs as a source of radiation in a lithographicapparatus has been proposed. In particular, the use of an array of LEDshas been proposed as a radiation source for providing 365 nm (I-line)radiation. However, the peak intensity of an emission spectrum of an LEDis known to drift, or in other words fluctuate. Such drift orfluctuation can occur for one of a number of reasons. For example, suchdrift or fluctuation can occur due to a temperature change of the LED, achange in the current with which the LED is driven, and/or generaldegradation over time of the LED. Furthermore, in an array of LEDs thewavelength or frequency at which the peak intensity of the emissionspectrum occurs may vary between LEDs in the array. As a result, thebandwidth of a radiation source including an array of LEDs will belarger then the bandwidth of an individual LED. If the emission spectraof LEDs within the array are not consistent, there may be associatednegative effects on the imaging quality of patterns applied to asubstrate. Such negative effects could arise since the lithographicapparatus may be configured to receive, transmit, reflect, etc radiationhaving a specific wavelength. Therefore, a change in the wavelength atwhich the peak emission occurs from the array of LEDs can lead todegradation in the reception, transmission, reflection, etc. of theradiation in the lithographic apparatus. A change in the wavelength atwhich the peak emission occurs from the array of LEDs may also affectthe application of patterns to a later of radiation sensitive material,since such material may only be sensitive (e.g., photoreactive) toradiation of a specific wavelength or narrow range of wavelengths.

It is desirable to provide, for example, a lithographic apparatus andmethod that obviates or mitigates one or more of the problems of theprior art referred to above.

SUMMARY

This section is for the purpose of summarizing some aspects of thepresent invention and to briefly introduce some preferred embodiments.Simplifications or omissions may be made to avoid obscuring the purposeof the section. Such simplifications or omissions are not intended tolimit the scope of the present invention.

A first embodiment of the present invention provides a lithographicapparatus including at least the following elements. An illuminationsystem provides a beam of radiation from radiation received from aradiation source. The radiation source includes an array of individuallycontrollable elements, each individually controllable element beingcapable of emitting radiation. A support structure supports a patterningdevice. The patterning device imparts the radiation beam with a patternin its cross-section. A projection system for projecting the patternedradiation beam onto a target portion of a substrate held in place by asubstrate table. A radiation peak intensity detection apparatus isconfigured to detect a peak in the intensity of an emission spectrum ofone or more individually controllable elements of the radiation source.

In one example, the lithographic apparatus may be provided with theradiation source. The illumination system may be provided with theradiation source. The radiation source may be located in a pupil planeof the illuminator, or adjacent to a pupil plane of the illuminator.

In one example, the individually controllable elements of the radiationsource may be configured to emit radiation that has a peak emissionwavelength in the UV, EUV, or beyond EUV range of the electromagneticspectrum.

In one example, the peak in the emission spectrum may be associated withan emission wavelength or frequency at which the intensity of theemission spectrum is the highest.

In one example, the radiation peak intensity detection apparatus may belocated in a position where radiation emitted by any one element of thearray is incident upon the radiation peak intensity detection apparatus.The radiation peak intensity detection apparatus may be moveable intoand out of the position.

In one example, the radiation peak intensity detection apparatus may bemoveable between positions which are adjacent to the elements of thearray. The radiation peak intensity detection apparatus may be moveablebetween positions which are adjacent to the elements of the array, suchthat the radiation peak intensity detection apparatus can be moved to aposition where the emission spectrum of a specific individuallycontrollable element can be detected. Alternatively, radiation emittedby individual elements of the array may be collected by a moveable fiberand directed to a sensor at a fixed location.

In one example, the radiation peak intensity detection apparatus mayinclude the following elements. One or more radiation intensitydetectors, each radiation detector being associated with a filter thatis located in a position whereby radiation emitted by an individuallycontrollable element of the radiation source passes through the filterbefore being detected by the radiation intensity detector.

In one example, the radiation peak intensity detection apparatus mayinclude an odd number of radiation intensity detectors, each radiationdetector being associated with a filter that is located in a positionwhereby radiation emitted by an individually controllable element of theradiation source passes through the filter before being detected by theradiation intensity detector. Each filter may have a different centralpass-frequency or pass-wavelength. One filter may have a centralpass-frequency or pass-wavelength which corresponds to a desiredfrequency or wavelength.

In one example, the apparatus may further include a control module forcontrolling the individually controllable elements of the radiationsource.

In various embodiments, the control module may form part of theradiation source or form a part of the radiation peak intensitydetection apparatus, or may be an independent piece of apparatus. Thecontrol module may be arranged to control a property that is used tocontrol each of the individually controllable elements. The controlmodule may be arranged to vary a property that is used to control theindividually controllable elements. The control module may be arrangedto control a property that is used to control the individuallycontrollable elements, the property being a specific property whichensures that an individually controllable element being controlled has adesired peak in its emission spectrum. The control module may bearranged to determine the specific property, or is provided withinformation related to the specific property. The property may be acurrent provided to each individually controllable element.

In one example, one or more of the individually controllable elementsmay be associated with a plurality of optical elements for changing anemission profile of the one or more individually controllable elements.The one or more individually controllable elements may be provided withthe plurality of optical elements. The plurality of optical elements maybe located adjacent to the one or more individually controllableelements. The plurality of optical elements may be diffractive,reflective or refractive.

In one example, the individually controllable elements may be LEDs orlaser diodes.

A second embodiment of the invention provides a method of detectingproperties of a radiation source that is used in connection with alithographic apparatus, or provided in the lithographic apparatus, theradiation source including an array of individually controllableelements, each individually controllable element being capable ofemitting radiation, the method including the following steps:

varying a property that is used to control an individually controllableelement;

detecting the intensity of radiation emitted by the individuallycontrollable element as the property is varied in order to identifychanges in the intensity of an emission spectrum of the individuallycontrollable element as the property is varied; and

determining a specific property (or in other words, value or magnitudeof this property) for which the peak in the intensity of an emissionspectrum of the element is a desired peak.

In one example, the method may further include controlling theindividually controllable element using the specific property. Theindividually controllable element may be controlled using the specificproperty during the exposure of a target portion of a substrate.

In one example, the method may further include repeating the method fora plurality of individually controllable elements of the array, or forall individually controllable elements of the array.

In one example, before detecting radiation emitted by the individuallycontrollable element as the property is varied, the method may furtherinclude moving a detector into a position where radiation emitted by theindividually controllable element can be detected so that the detectionmay be undertaken. Alternatively, radiation emitted by individualelements of the array may be collected by a moveable fiber and directedto a sensor at a fixed location.

In one example, the desired peak may be when the intensity of theemission spectrum is highest at a desired wavelength or frequency. Mostpreferably, the intensity of the emission spectrum of all elements ofthe array will be highest at the same desired wavelength or frequency.

According to a third embodiment of the invention, there is provided alithographic arrangement including the following elements. A radiationsource. The radiation source including an array of individuallycontrollable elements, each element being capable of emitting radiation.An illumination system for providing a beam of radiation from radiationreceived from the radiation source. A support structure for supporting apatterning device. The patterning device serving to impart the radiationbeam with a pattern in its cross-section. A substrate table for holdinga substrate. A projection system for projecting the patterned radiationbeam onto a target portion of the substrate. A control module for theradiation source. The control module being arranged to selectivelyprevent all radiation emitted by the individually controllable elementsof the radiation source from passing through the lithographic apparatusby preventing all of the individually controllable elements of theradiation source from emitting radiation.

According to a fourth embodiment of the invention, there is provided amethod of including the following steps. Providing a substrate. Using anarray of individually controllable elements, each element being capableof emitting radiation, to provide a source of radiation. Using anillumination system to provide a beam of radiation from radiationreceived from the source of radiation. Using a patterning device toimpart the radiation beam with a pattern in its cross-section.Projecting the patterned radiation beam onto a target portion of thesubstrate. Selectively preventing all radiation emitted by theindividually controllable elements of the radiation source from passingthrough the lithographic apparatus by preventing all of the individuallycontrollable elements of the radiation source from emitting radiation.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate one or more embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIGS. 1A and 1B schematically depict lithographic apparatus, accordingto embodiments of the invention.

FIGS. 2 a and 2 b schematically depict a radiation source including anarray of LEDs.

FIGS. 3 a and 3 b schematically depict an illuminator of a lithographicapparatus including an array of LEDs.

FIGS. 4 a and 4 b schematically depict the emissions spectrum of theLEDs of the arrays shown in and described with reference to FIGS. 2 a to3 b.

FIGS. 5 a and 5 b schematically depict the overall emission profile ofthe arrays shown in and described with reference to FIGS. 2 a to 4 b.

FIG. 6 a schematically depicts a radiation peak intensity detectionapparatus and its location relative to a radiation beam, in accordancewith an embodiment of the present invention.

FIG. 6 b schematically depicts the location of a radiation peakintensity detection apparatus and its location relative to a radiationbeam and a substrate table, in accordance with an embodiment of thepresent invention.

FIG. 7 schematically depicts a radiation peak intensity detectionapparatus that is moveable in front of an array of LEDs, in accordancewith an embodiment of the present invention.

FIG. 8 schematically depicts a radiation peak intensity detectionapparatus, in accordance with an embodiment of the present invention.

FIG. 9 schematically depicts a control arrangement for controlling anarray of LEDs, in accordance with an embodiment of the presentinvention.

FIG. 10 schematically depicts an LED.

FIGS. 11 a and 11 b schematically depict LEDs provided with, or locatedadjacent to a plurality of optical elements, in accordance with anembodiment of the present invention.

Features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

The invention will be better understood from the following descriptionsof various “embodiments” of the invention. Thus, specific “embodiments”are views of the invention, but each does not itself represent the wholeinvention. In many cases individual elements from one particularembodiment may be substituted for different elements in anotherembodiment carrying out a similar or corresponding function. The presentinvention relates to

The embodiment(s) described, and references in the specification to “oneembodiment,” “an embodiment,” “an example embodiment,” etc., indicatethat the embodiment(s) described can include a particular feature,structure, or characteristic, but every embodiment cannot necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to effect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Embodiments of the invention can be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention canalso be implemented as instructions stored on a machine-readable medium,which can be read and executed by one or more processors. Amachine-readable medium can include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium can includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other forms of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.), and others. Further,firmware, software, routines, instructions can be described herein asperforming certain actions. However, it should be appreciated that suchdescriptions are merely for convenience and that such actions in factresult from computing devices, processors, controllers, or other devicesexecuting the firmware, software, routines, instructions, etc.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g., having a wavelength in the range of5-20 nm).

The term “patterning device” used herein should be broadly interpretedas referring to a device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate. Generally, the patternimparted to the radiation beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

A patterning device may be transmissive or reflective. Examples ofpatterning device include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned.

FIGS. 1A and 1B schematically depict lithographic apparatus 100 andlithographic apparatus 100′, respectively. Lithographic apparatus 100and lithographic apparatus 100′ each include: an illumination system(illuminator) IL configured to condition a radiation beam B and PB, inFIGS. 1A and 1B, respectively (the radiation beam may be, for example,DUV or EUV radiation); a support structure (e.g., a mask table) MTconfigured to support a patterning device (e.g., a mask, a reticle, or adynamic patterning device) MA and connected to a first positioner PMconfigured to accurately position the patterning device MA; and asubstrate table (e.g., a wafer table) WT configured to hold a substrate(e.g., a resist coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate W. Lithographicapparatuses 100 and 100′ also have projection systems PS and PL,respectively configured to project a pattern imparted to the radiationbeam B or PB by patterning device MA onto a target portion (e.g.,including one or more dies) C of the substrate W. In lithographicapparatus 100 the patterning device MA and the projection system PS arereflective, and in lithographic apparatus 100′ the patterning device MAand the projection system PL are transmissive.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling the radiation B, PB.

The support structure MT holds the patterning device MA in a manner thatdepends on the orientation of the patterning device MA, the design ofthe lithographic apparatuses 100 and 100′, and other conditions, such asfor example whether or not the patterning device MA is held in a vacuumenvironment. The support structure MT may use mechanical, vacuum,electrostatic or other clamping techniques to hold the patterning deviceMA. The support structure MT may be a frame or a table, for example,which may be fixed or movable, as required. The support structure MT mayensure that the patterning device is at a desired position, for examplewith respect to the projection system PS or PL.

The term “patterning device” MA should be broadly interpreted asreferring to any device that may be used to impart a radiation beam B,PB with a pattern in its cross-section, such as to create a pattern inthe target portion C of the substrate W. The pattern imparted to theradiation beam B may correspond to a particular functional layer in adevice being created in the target portion C, such as an integratedcircuit.

The patterning device MA may be transmissive (as in lithographicapparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus100 of FIG. 1A). Examples of patterning devices MA include reticles,masks, programmable mirror arrays, and programmable LCD panels. Masksare well known in lithography, and include mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. An example of a programmable mirror array employs amatrix arrangement of small mirrors, each of which may be individuallytilted so as to reflect an incoming radiation beam in differentdirections. The tilted mirrors impart a pattern in the radiation beam Bwhich is reflected by the mirror matrix.

The term “projection system” may encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment may be used for EUV or electron beamradiation since other gases may absorb too much radiation or electrons.A vacuum environment may therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ may be ofa type having two (dual stage) or more substrate tables (and/or two ormore mask tables) WT. In such “multiple stage” machines the additionalsubstrate tables WT may be used in parallel, or preparatory steps may becarried out on one or more tables while one or more other substratetables WT are being used for exposure.

Referring to FIGS. 1A and 1B, the illuminator IL receives a radiationbeam from a radiation source SO. The source SO and the lithographicapparatuses 100, 100′ may be separate entities, for example when thesource SO is an excimer laser. In such cases, the source SO is notconsidered to form part of the lithographic apparatuses 100 or 100′, andthe radiation beam B passes from the source SO to the illuminator ILwith the aid of a beam delivery system BD (FIG. 1B) including, forexample, suitable directing mirrors and/or a beam expander. In othercases, the source SO may be an integral part of the lithographicapparatuses 100, 100′—for example when the source SO is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AM (FIG. 1B) for adjustingthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator may be adjusted. In addition, theilluminator IL may include various other components (FIG. 1B), such asan integrator IN and a condenser CO. The illuminator IL may be used tocondition the radiation beam B, to have a desired uniformity andintensity distribution in its cross section.

Referring to FIG. 1A, the radiation beam B is incident on the patterningdevice (e.g., mask) MA, which is held on the support structure (e.g.,mask table) MT, and is patterned by the patterning device MA. Inlithographic apparatus 100, the radiation beam B is reflected from thepatterning device (e.g., mask) MA. After being reflected from thepatterning device (e.g., mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the radiation beam B onto atarget portion C of the substrate W. With the aid of the secondpositioner PW and position sensor IF2 (e.g., an interferometric device,linear encoder or capacitive sensor), the substrate table WT may bemoved accurately, e.g. so as to position different target portions C inthe path of the radiation beam B. Similarly, the first positioner PM andanother position sensor IF1 may be used to accurately position thepatterning device (e.g., mask) MA with respect to the path of theradiation beam B. Patterning device (e.g., mask) MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterningdevice (e.g., mask MA), which is held on the support structure (e.g.,mask table MT), and is patterned by the patterning device. Havingtraversed the mask MA, the radiation beam B passes through theprojection system PL, which focuses the beam onto a target portion C ofthe substrate W. With the aid of the second positioner PW and positionsensor IF (e.g., an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1B) can be used to accuratelyposition the mask MA with respect to the path of the radiation beam B,e.g., after mechanical retrieval from a mask library, or during a scan.

In general, movement of the mask table MT may be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WT may be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner)the mask table MT may be connected to a short-stroke actuator only, ormay be fixed. Mask MA and substrate W may be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (knownas scribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the mask MA, the mask alignment marks may belocated between the dies.

The lithographic apparatuses 100 and 100′ may be used in at least one ofthe following modes:

1. In step mode, the support structure (e.g., mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam B is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C may be exposed.

2. In scan mode, the support structure (e.g., mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam B is projected onto a target portion C (i.e., asingle dynamic exposure). The velocity and direction of the substratetable WT relative to the support structure (e.g., mask table) MT may bedetermined by the (de-)magnification and image reversal characteristicsof the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is keptsubstantially stationary holding a programmable patterning device, andthe substrate table WT is moved or scanned while a pattern imparted tothe radiation beam B is projected onto a target portion C. A pulsedradiation source SO may be employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation may be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use may also be employed.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Further, the terms “radiation” and “beam” used herein encompass alltypes of electromagnetic radiation, including ultraviolet (UV) radiation(e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm), extremeultra-violet (EUV or soft X-ray) radiation (e.g., having a wavelength inthe range of 5-20 nm, e.g., 13.5 nm), or hard X-ray working at less than5 nm, as well as particle beams, such as ion beams or electron beams.Generally, radiation having wavelengths between about 780-3000 nm (orlarger) is considered IR radiation. UV refers to radiation withwavelengths of approximately 100-400 nm. Within lithography, it isusually also applied to the wavelengths, which can be produced by amercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or I-line 365nm. Vacuum UV, or VUV (i.e., UV absorbed by air), refers to radiationhaving a wavelength of approximately 100-200 nm. Deep UV (DUV) generallyrefers to radiation having wavelengths ranging from 126 nm to 428 nm,and in an embodiment, an excimer laser can generate DUV radiation usedwithin lithographic apparatus. It should be appreciated that radiationhaving a wavelength in the range of, for example, 5-20 nm relates toradiation with a certain wavelength band, of which at least part is inthe range of 5-20 nm.

FIG. 2 a schematically depicts a radiation source SO in side view, forexample the radiation source shown in and described with reference toFIG. 1A or 1B. The radiation source SO includes a two-dimensional array(16×16) of individually controllable elements that are capable ofemitting radiation 2. Only sixteen elements are shown, because theFigure is a side view of the array. In this embodiment, the elements areLEDs 4. The Figure shows that the array of LEDs 2 includes 16×16 LEDs 4.This number of LEDs 4 is given by way of example only, and in practicethe number of LEDs forming the array may be, for instance, a few hundredLEDs, or even a few thousand LEDs.

As discussed above, the radiation source SO may form part of alithographic apparatus, or the lithographic may be arranged to receiveradiation from a radiation source SO external to the lithographicapparatus.

In FIG. 2 a, the source SO is shown in a configuration where the LEDs 4of the array 2 are not emitting radiation. In contrast, in FIG. 2 b, thesource SO is shown in side view as being in a configuration where theLEDs 4 of the array 2 are emitting radiation (indicated in the Figure bythe LEDs 4 being shaded). Referring to FIGS. 2 a and 2 b in combination,the radiation source SO can be controlled to selectively prevent allradiation emitted by the LEDs 4 of the radiation source SO from passingthrough the lithographic apparatus by preventing all of the LEDs 2 ofthe radiation source from emitting radiation. Selectively prevent, inthis context, does not mean that the lithographic apparatus iscompletely inactive. Instead, selectively prevent means that radiationmay be selectively prevented from passing through the lithographicapparatus for relatively short periods of time, for example when asubstrate is being moved so that a different target potion may beexposed to radiation. It will be appreciated that in this respect thecontrol of the array of LEDs 2 serves as a shutter for the lithographicapparatus. Since the LEDs can be activated or deactivated (or in otherwords, controlled to emit radiation, or control to stop emittingradiation) at a high speed, control of the LEDs may replace the need toprovide the lithographic apparatus with a mechanical shutter or thelike. Furthermore, a mechanical shutter may, over time, become worn ordamaged due to repeated actuation. The speed of actuation may be reducedif the shutter needs to be capable of withstanding prolonged exposure toEUV radiation, for example. This is because the shutter may need to beformed from a heavy duty material suitable for withstanding prolongedexposure to EUV radiation, for example. By preventing the all of theLEDs from emitting radiation, no mechanical actuation is required toblock the radiation. There is no need to block or suppress EUVradiation, for example, for a prolonged period of time. This may reducecontamination due to which might otherwise results from, for example,degradation of a mechanical shutter by EUV radiation.

FIG. 3 a schematically depicts in side view an illuminator IL, forexample the illuminator shown in and described with reference to FIG. 1Aor 1B. The Figure shows that the illuminator IL is provided with anarray (16×16) of LEDs 2. Only sixteen LEDs are shown, because the Figureis a side view of the array. The array of LEDs 2 is shown as including16×16 LEDs 4. However, any number of LEDs 4 may form the array 2, and inpractice the array 2 may include, for instance, a few hundred or even afew thousand LEDs.

By providing the illuminator IL with an array of LEDs 2, there is noneed to provide the lithographic apparatus with another source ofradiation. The array of LEDs 2 in the illuminator IL may serve as thesingle and only source of radiation in the lithographic apparatus. Thearray of LEDs 2 in the illuminator IL may also function as a shutter, asdescribed above in relation to FIGS. 2 a and 2 b.

One or more LEDs 4 of the array 2 may be selectively controlled to emitradiation or not emit radiation. Such selective control may be used toregulate, for example, the total energy or intensity profile of theradiation generated by the array 2 as a whole. The angular intensitydistribution of radiation emitted by the array 2 can be controlled byselectively re-directing the radiation using, for example, an array ofindividually controllable elements such as mirrors or diffractingelements, or by using one or more diffractive optical elements or thelike. Alternatively, the control of the angular intensity distributionof the radiation emitted by the array 2 can be achieved by selectingspecific patterns or configurations of LEDs 4 of the array 2 to emitradiation. This can be achieved by locating the array 2 in or adjacentto a pupil plane 6 of the illuminator. Additional optical components(not shown) may be provided between the array of LEDs 2 and the pupilplane 6 in order to couple radiation emitted by the array 2 into thatpupil plane 6. A micro lens array is an example of such an opticalcomponent. Further optical components 8 may be used to, for example,homogenize the radiation emitted by the array 2. A quartz rod is anexample of such an optical component.

FIG. 3 b schematically depicts an example of how the array 2 can becontrolled to create a specific angular intensity distribution,sometimes referred to as an illumination mode. FIG. 3 b the array 2 inan end-on view, so that all sixteen LEDs 4 of the array 2 are visible.FIG. 3 b shows that only a sub-set 10 of the LEDs 4 of the array 2 arecontrolled to emit radiation. This subset of LEDs 10 is configured toform four regions of emission that are located in each corner of thearray 2. The regions of emission form what is known in the art as a“quadrapole” illumination mode. Other illumination modes can becontrolled by selecting one or more different sub-sets of LEDs 4 to emitradiation. For example, an annular illumination mode could be created bycontrolling a sub-set of LEDs 4 that are in an annular configuration toemit radiation.

The remainder of this description will refer to the array of LEDs, andthe LEDs that are part of that array, in general. The description isthus equally applicable to the array of LEDs when it is located in theilluminator of a lithographic apparatus, when the array forms the sourcein a lithographic apparatus, or when the array forms the source for alithographic apparatus.

FIG. 4 a depicts a desirable emission profile 20 for the array of LEDsdescribed above. The emission profile of the array is desirable in thatall of the LEDs of the array have the same emission profile (thus, onlya single emission profile is shown in the Figure). The emissionbandwidth of the array is thus narrow. Such a desirable emission profile20 is only achievable if the individual emission profiles of each LED 22are substantially uniform and consistent across the array. In practice,this is difficult to achieve or maintain.

As discussed above, the wavelength (or frequency) at which a peak in theemission intensity of radiation emitted by an LED depends on thetemperature of the LED, the current applied to the LED, any degradationof the LED, and also possible manufacturing differences betweendifferent LEDs. Therefore, even if it is possible to ensure that at aspecific time the emission profile of the LEDs in the array is uniformand consistent across the array, there is no guarantee that suchuniformity and consistency will be maintained over any given period oftime. This is undesirable.

FIG. 4 b illustrates the overall emission profile of the array of LEDsafter a period of time 24. It can be seen that there is a stark contrastbetween the emission profile across the array of LEDs after a period oftime 24, and the desired emission profile across LEDs shown in anddescribed with reference to FIG. 4 a. Referring back to FIG. 4 b, theemission profile of each LED within the array 26 no longer peaks at thesame wavelength. The emission bandwidth of the array is thus broaderthan that shown in FIG. 4 a. Such inconsistency between the peakemission wavelengths may arise due to the reasons given above (e.g.,temperature changes, current changes, etc.).

FIGS. 5 a and 5 b summarize the situations described in relation toFIGS. 4 a and 4 b. FIG. 5 a shows the desired emission profile acrossthe array of LEDs 20. FIG. 5 b shows how, over time, the desiredemission profile may degrade or change into a non-uniform emissionprofile across the array 24. In other words, the LEDs of the array willnot all be emitting radiation at the same desired peak wavelength. It isdesirable to ensure that radiation emitted by the array as a whole andhas a profile which is substantially the same as that shown in FIG. 5 a,as opposed to the profile shown in FIG. 5 b. Presently, however, and foran LED array used in or in connection with a lithographic apparatus, nomethod or apparatus has been proposed for identifying a change in thewavelength at which peak intensity emission of the LEDs of the arrayoccurs, and using this identification to control the LEDs and modify theoutput of the LED array as a whole such that it has a more uniformemission profile.

According to an embodiment of the present invention, there is provided alithographic apparatus which has a radiation peak intensity detectionapparatus for detecting a peak in the intensity of an emission spectrumof an LED of the array of LEDs. A control module (for example, providedin the radiation peak intensity detection apparatus or in a controllerof the LEDs) is able to process information related to the detected peak(e.g., the frequency or wavelength at which the peak occurs), and tocontrol the LED or LEDs in order to ensure that the emission profile ofthe array of LEDs as a whole is more uniform. A feedback loop is thiscreated. Additionally or alternatively, such detection of the peak maybe undertaken when the lithographic apparatus is in operation, or duringa downtime of the lithographic apparatus. The detection mayalternatively or additionally be used as a calibration routine. A moreuniform emission profile of the array of LEDs is advantageous, since itallows the array of LEDs to be tuned to a desired peak, for example apeak intensity at a certain wavelength or frequency. The desired peakmay have a wavelength which the lithographic apparatus and/or the resiston the substrate is designed for. Tuning (or in other words adjustment)of the peaks of the LEDs and the array of LEDs as a whole may allow forimproved imaging of patterns on a resist coated substrate, or themaintenance of a certain quality or level of imaging.

The radiation peak intensity detection apparatus may be fixed inposition relative to the lithographic apparatus. The radiation peakintensity detection apparatus may be placed in a location for whichradiation emitted by any one of the LEDs of the array is incident uponthe radiation peak intensity detection apparatus. This is so that anyone of the LEDs of the array can be controlled to emit radiation, andthe radiation peak intensity detection apparatus can then detectproperties of the radiation emitted by that one LED. The radiation peakintensity detection apparatus may not be fixed in position, and caninstead be moveable into the position at which radiation emitted by anyone of the LEDs of the array can be detected. Alternatively, theradiation peak intensity detection apparatus may be moveable into one ormore positions where the emission of one or more specific LEDs may bedetected. For instance, the radiation peak intensity detection apparatusmay be moveable in front of the array of LEDs and positioned in front ofone (or in other examples, one or more) of the LEDs of the array inorder to determine properties of that LED's emission profile. Specificexamples of the use, location and design of the radiation peak intensitydetection apparatus will now be described with reference to FIGS. 6 a, 6b, 7 and 8.

FIG. 6 a schematically depicts a radiation peak intensity detectionapparatus 30. The radiation peak intensity detection apparatus 30 isshown as being located at an intermediate focus 31 of a radiation beam32 of a lithographic apparatus (for example the lithographic apparatusshown in and described with reference to FIG. 1). This could forinstance be in the reticle plane of the lithographic apparatus. In oneexample, the radiation beam 32 may contain radiation emitted by one ormore of the LEDs or the array described above. Since the radiation peakintensity detection apparatus 30 is located at the intermediate focus31, the radiation peak intensity detection apparatus 30 can detectradiation emitted by any one or more of the LEDs of the array. Thismeans that by selectively controlling only a single LED of the array toemit radiation, properties of the emission profile of that LED (and thatLED alone) can be determined. In one example, the radiation peakintensity detection apparatus 30 is moveable into and out of theintermediate focus. This is so that when the radiation peak intensitydetection apparatus 30 is not being used, it does not affect thepropagation of the radiation beam 32 through the lithographic apparatus.

The radiation peak intensity detection apparatus may be located in anarea of the lithographic apparatus where radiation from all of the LEDsof the arrays incident, but which does not affect the propagation of theradiation beam through the lithographic apparatus. For instance, theradiation peak intensity detection apparatus may be located in aposition where radiation emitted by the array of LEDs is incident, butnot used to pattern a substrate. For example, the radiation peakintensity detection apparatus may be located in an area of thelithographic apparatus where radiation is scattered or reflected, or onor in a patterning device, a patterning device holder, or a substrateholder.

FIG. 6 b schematically depicts another example of a possible location ofthe radiation peak intensity detection apparatus. In this example, theradiation peak intensity detection apparatus 30 is located in asubstrate table WT, for example the substrate table shown in anddescribed with reference to FIG. 1A or 1B. The radiation peak intensitydetection apparatus 30 will function in the same manner as described inrelation to FIG. 6 a. The substrate table WT may be moved such that aradiation beam 32 is incident upon the radiation peak intensitydetection apparatus 30, for example when patterns are not being appliedto a substrate located on the patterning device.

Although FIG. 6 b describes the location of the radiation peak intensitydetection apparatus 30 relative to a substrate table WT, the radiationpeak intensity detection apparatus 30 could equally be located in or ona patterning device, or a holder for a patterning device. The patterningdevice and/or the patterning device holder may be moved to bring theradiation peak intensity detection apparatus 30 into a position wherethe radiation beam 32 is incident upon it.

In FIGS. 6 a and 6 b, the radiation peak intensity detection apparatushas been shown as being fixed in a position which allows properties ofthe emission spectrum of any one of the LEDs of the array to bedetermined, or being moveable into and out of such a position. Inanother example, the radiation peak intensity detection apparatus may bemoved into one or more positions whereby the properties of the emissionspectrum of one or more specific LEDs of the array may be determined.FIG. 7 shows such an example.

FIG. 7 schematically depicts the radiation peak intensity detectionapparatus 30, according to one embodiment of the present invention. Theradiation peak intensity detection apparatus 30 is moveable in an Xdirection along a first support 40. The radiation peak intensitydetection apparatus 30 may be moveable along the first support 40 usingmotors, linear actuators, or any other suitable configuration. The firstsupport 40 is in connection with two second supports 42 which extendsubstantially in the Y direction. The first support 40 is moveable alongthese second supports 42, such that the first support 40 is moveable inthe Y direction. The first support 40 may be moveable along the secondsupports 42 using one or more motors, linear actuators or any othersuitable configuration. Since the radiation peak intensity detectionapparatus 30 is moveable along the first support 40 in the X direction,and since the first support 40 is moveable in the Y direction along thesecond supports 42, it will be understood that the radiation peakintensity detection apparatus 30 may be moved in the X and/or Ydirection.

FIG. 7 also schematically depicts the array of the LEDs 2 describedabove, according to an embodiment of the present invention. A detectingsurface or element of the radiation peak intensity detection apparatus30 is arranged to face the array of LEDs 2, such that a property of theradiation emitted by the LEDs 4 of the array 2 may be determined by theradiation peak intensity detection apparatus 30. The radiation peakintensity detection apparatus 30 is moveable around the array by movingthe radiation peak intensity detection apparatus 30 in the X and/or Ydirection. The radiation peak intensity detection apparatus 30 ismoveable to any specific location relative to the array 2, such that aproperty of the emission profile of one or more specific LEDs 4 of thearray 2 can be determined. For instance, the radiation peak intensitydetection apparatus may be configured and/or positioned such that it canonly receive radiation emitted by a single LED 4. Alternatively, theradiation peak intensity detection apparatus 30 can be configured suchthat it can receive radiation from more than one LED 4. In general, theradiation peak intensity detection apparatus 30 is moveable betweenpositions which are adjacent to the LEDs 4 of the array 2, such that theradiation peak intensity detection apparatus 30 can be moved to aposition where the emission spectrum of a specific LED (or one of agroup of LEDs) can be detected.

By controlling the LEDs 4 of the array 2 to emit radiation, theradiation peak intensity detection apparatus 30 can be moved around thearray to determine a property of the emission profile of one or morespecific LEDs of the array. The detection of a property may be madeeasier if only one or a selection of LEDs are controlled to emitradiation at any one time.

In one example, the radiation peak detection may include one or moreoptical fibers that are moveable into and out of the path of radiationemitted by one or more LEDs of the array. The one or more optical fibersmay be coupled to a photo detector or the like that is fixed inposition, and which is not located in a path of radiation emitted by oneor more LEDs of the array.

The radiation peak intensity detection apparatus referred to above canbe any apparatus capable of detecting the peak in the intensity of anemission spectrum of radiation emitted by the LEDs, and/or changes inthis peak, and the wavelength (or a range of wavelengths) or thefrequency (or a range of frequencies) at which this peak occurs. Theradiation peak intensity detection apparatus could therefore be, forexample, a spectrometer. A spectrometer is capable of determining thepeak intensity of an emission spectrum of radiation.

FIG. 8 schematically depicts a radiation peak intensity detectionapparatus 30, in accordance with an embodiment of the present invention.The radiation peak intensity detection apparatus 30 includes a housing50. The housing 50 is provided with an opening 52, through whichradiation may enter the radiation peak intensity detection apparatus 30.The opening 52 may be, or may be provided with, a lens 4. The lens maybe used for collecting, gathering, focusing, etc radiation.Alternatively or additionally, the opening 52 may be provided with amembrane or other covering for preventing any particles or contaminationentering the housing 50.

Located within the housing 50 are three radiation intensity detectors: afirst radiation intensity detector 56, a second radiation intensitydetector 58, and a third radiation intensity detector 60. The radiationdetectors 56, 58 and 60 may be, for example, photo diodes which aresensitive to radiation emitted by the LEDs, or the like. Located infront of each of the radiation intensity detectors 56, 58 and 60 is afilter, e.g., a narrow band filter (e.g., an about 2-3 nm band-passfilter). Located in front of the first radiation intensity detector 56is a first narrow-band filter 62. Located in front of the secondradiation intensity detector 58 is a second narrow-band filter 64.Located in front of the third radiation intensity detector 60 is a thirdnarrow-band filter 66. Each of the narrow-band filters 62, 64, 66 has adifferent central pass-wavelength (or frequency). The centralpass-wavelength of each of the narrow-band filters 62, 64, 66 areseparated (or in other words shifted) by about 2-3 nm. Since thenarrow-band filters 62, 64, 66 each have a different band-pass of about2-3 nm, the three narrow-band filters 62, 64, 66 together cover a rangeof about 6-9 nm. In one example, at least one of the narrow-band filtershas a central pass-wavelength which is equal to the desired peakintensity output of the LEDs (e.g., about 365 nm). Thus, a possibleconfiguration for the narrow-band filters 62, 64, 66 is that the firstnarrow-band filter 62 has a central pass-wavelength of about 362 nm, thesecond narrow-band filter 64 has a central pass-wavelength of about 365nm, and the third narrow-band filter 66 has a central pass-wavelength ofabout 368 nm.

Since each of the narrow-band filters 62, 64, 66 has a band-passwavelength which is different from all of the other filters, 62, 64, 66and because one of the narrow-band filters contains the central-passwavelength which is desired, it is possible to detect changes in thepeak intensity of the emission spectrum of an LED. Because an odd numberof filters 62, 64, 66 are used, it is possible to easily track changesin the wavelength at which peak emission occurs, and to control thediodes to ensure that the peak is centered on the desired peak byensuring that the maximum intensity is measured by the detector which islocated by the filter which is sensitive to the desired frequency ofwavelength.

Although the use of three radiation intensity detectors has beendescribed, each detector being associated (e.g., provided with) a filterhaving a different pass-wavelength, other arrangements are possible. Forexample, one or more radiation intensity detectors may be provided, eachradiation detector being associated with a filter that is located in aposition whereby radiation emitted by an LED of the array passes throughthe filter before being detected by the radiation intensity detector. Asdescribed above, an odd number of radiation intensity detectors, eachdetector being associated (e.g., provided with) a filter having adifferent pass-wavelength, may be advantageous.

The radiation peak intensity detection apparatus 30 described in theFigure is simpler, smaller and cheaper to construct and maintain than aspectrometer. A peak in an emission profile may also be determined morerapidly using the described radiation peak intensity detection apparatus30 than with a spectrometer.

Each of the radiation intensity detectors 56, 58, 60 is provided with anoutput 68, 70, 72. Each of the outputs 68, 70, 72 may be in connectionwith (or in other words provided to) a control module. The controlmodule may be configured to control the LEDs of the array in order to,for example, take into account changes in the peak intensity of theemission spectra of the LEDs. The control module may form a part of theradiation source, form a part of the radiation peak intensity detectionapparatus, or may be an independent piece of apparatus. An example of acontrol module and its functionality is described in relation to FIG. 9.

FIG. 9 schematically depicts an exemplary control module 80. The controlmodule 80 is shown as being arranged to receive the outputs 68, 70, 72from the radiation intensity detectors shown in and described withreference to FIG. 8. Referring back to FIG. 9, the control module 80 isalso configured to receive a further input 82. The further input 82 mayprovide the control module 80 with information regarding, for example,the ambient temperature, the temperature of the array of LEDs, thetemperature of one or more LEDs within the array, and the required ordesired frequency or wavelength for the peak emission of the LEDs of thearray. The control module 80 is in connection with 84 drivers for eachLED, for example LED₁, LED₂, . . . LED_(N) (where N is the total numberof LEDs in the array). Alternatively, the control module 80 may be indirect connection with each LED.

Using the information provided by the radiation intensity detectors andthe information provided by the further input 82, the control module isable to control the LEDs via the LED driver circuitry LED₁-LED_(N) tocontrol the LEDs to ensure that the emission spectra of the LEDs have apeak intensity at a wavelength or frequency or which coincides with adesired wavelength or frequency.

In use, a single LED may be controlled to emit radiation. The radiationpeak intensity detection apparatus will detect at least a part of theemission profile of the radiation emitted by this LED and provide thisinformation to the control module. The control module will vary (e.g.,undertake a sweep of) a first property (e.g., current and/or voltage)that is used to control the LED. In this embodiment, the current isvaried. The control module will then determine the current for which themaximum intensity is measured by the peak radiation intensity detectorthat is provided with the narrow-band pass filter which corresponds tothe desired output of the LED (for example 365 nm). When a peak inintensity has been detected at this detector, the magnitude of thecurrent used to achieve this peak is stored for future reference andcontrol of the LED, or is used within a short period of time to controlthe LED. This current is therefore a specific current, or a specific‘first property’, as described above.

This process is undertaken for all of the elements of the array in orderto determine what current is necessary to drive each of the LEDs of thearray which results in a peak intensity at a desired wavelength orfrequency. The temperature of each LED can also be taken into accountsuch that the peak intensity of the LED emission spectra is measured asa function of not only current, but also temperature. When all of therequired information has been gathered, the information can be used toprovide all of the LEDs with the current that is required to ensure thatall of the LEDs of the array have an emission spectra with a peakintensity at the desired wavelength or frequency.

In one example, as well as ensuring that the peak intensity of theemission spectra of each LED has a desired wavelength or frequency, theapparatus and methods referred to above may also be used to measure theintensity at that peak. This can be used to ensure that the intensity issubstantially constant for all LEDs across the array, thus ensuring thatthe LED array as a whole has a uniform emission profile and/or a desired(e.g., narrow) bandwidth. The emission intensity may also be a functionof the current used to control the LED, or another property used tocontrol the LED, such as the voltage.

In one example, the control module can determine the specific current(or more generally, a specific property) that is required to ensure thatthe LED has a desired peak in its emission spectrum. Alternatively oradditionally, the control module can be provided with informationrelated to such a specific current (or more generally, a specificproperty), for example the magnitude.

FIG. 10 schematically depicts an LED 90, according to one embodiment ofthe present invention. The LED is provided with a casing 92 that issubstantially transparent to radiation which the LED 90 is designed toemit (e.g., radiation having a peak emission at a wavelength of 365 nm).It is known that LEDs are Lambertian radiators, in that the profile ofthe emission follows the Cosine Emission Law (sometimes referred to asLambert's Emission Law). It is sometimes desirable to ensure that theemission profile of an LED is not Lambertian in nature.

According to an embodiment of the present invention, an LED is providedwith a plurality of, for example, lenses for transforming (or in otherwords changing) the Lambertian emission profile into a more desirableemission profile (for example a more cone-like, or in other wordsconical emission profile). The LED itself may be provided with integrala plurality of lenses, or the plurality of lenses may be providedadjacent to the LED.

FIG. 11 a shows an LED 100, according to an embodiment of the presentinvention. The LED is provided with a casing 102 that is substantiallytransparent to radiation that the LED is designed to emit (e.g.,radiation having a peak emission at a wavelength of about 365 nm). Thecasing 102 is provided with a plurality of lenses 104, 106, 108, 110which are designed to change the inherent Lambertian profile of the LED100 and make the emission profile of the LED 100 more desirable.

FIG. 11 b shows an LED 120, according to an embodiment of the presentinvention. The LED 120 is provided with a casing 122 that issubstantially transparent to radiation that the LED 120 is designed toemit (e.g., radiation having a peak emission at a wavelength of about365 nm). Located adjacent to the LED 120 are a plurality of lenses 124,126, 128, 130. The lenses 124, 126, 128, 130 are designed to change theinherent Lambertian profile of the LED 120 and make the emission profileof the LED 120 more desirable

Although the use of lenses has been described for changing theLambertian emission profile of an LED, any suitable optical element maybe used. For example, the LED may be provided with, or be locatedadjacent to, one or more reflective, refractive, diffractive, etc.,optical elements that are arranged to correct the Lambertian emissionprofile of the LED.

All of the above embodiments have been described in relation to the useof LEDs in an array. However, the invention is not limited to the use ofLEDs. With regard to the embodiments shown in and described withreference to FIGS. 2 to 9, the array of LEDs may be replaced by an arrayof any other individually controllable elements that are capable ofemitting radiation. For instance, the elements may be laser diodes. Withregard to the embodiments shown in and described with reference to FIGS.10, 11 a and 11 b, the use of one or more optical elements to correctand/or change the emission profile of an LED may additionally oralternatively be used in conjunction with other elements which arecapable for emitting radiation, for example a laser diode. Although theembodiments shown in and described with reference to FIGS. 10, 11 a and11 b have been described in relation to a single LED, the embodimentsare also applicable to arrays of LEDs or other elements capable toemitting radiation. For example, the plurality of lenses may be providedin each of the elements of the array, or can be provided in a sheet orthe like located adjacent to the array of elements. In any of thedescribed embodiments, an element that is capable of emitting radiationmay be configured to emit radiation that has a peak intensity in itsemission spectrum at a wavelength in the UV, EUV, or beyond EUV range ofthe electromagnetic spectrum. This may be advantageous, since UV, EUV,or beyond EUV radiation is commonly used in lithography.

In the above embodiments, the use of a control module has beendescribed. The control module can be anything capable of providing somesort of control. For example, the control module could be a computersystem, and embedded processor provided with an appropriate program, anoscilloscope, or the like.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. A lithographic apparatus comprising: an illumination system forproviding a beam of radiation from radiation received from a radiationsource, the radiation source comprising individually controllableelements, each individually controllable element being capable ofemitting radiation; a support structure for supporting a patterningdevice, the patterning device serving to impart the radiation beam witha pattern in its cross-section; a substrate table for holding asubstrate; a projection system for projecting the patterned radiationbeam onto a target portion of the substrate; and a radiation peakintensity detection apparatus configured to detect a peak in theintensity of an emission spectrum of one or more individuallycontrollable elements of the radiation source, wherein respectiveelements of the individually controllable elements are each associatedwith at least two corresponding optical elements, the correspondingoptical elements being provided on a substantially transparent casingintegrated with and surrounding the associated individually controllableelement.
 2. The apparatus of claim 1, wherein the radiation source islocated in a pupil plane of the illuminator, or adjacent to a pupilplane of the illuminator.
 3. The apparatus of claim 1, wherein theindividually controllable elements of the radiation source areconfigured to emit radiation that has a peak emission wavelength in theUV, EUV, or beyond EUV range of the electromagnetic spectrum.
 4. Theapparatus of claim 1, wherein the peak in the emission spectrum isassociated with an emission wavelength or frequency at which theintensity of the emission spectrum is the highest.
 5. The apparatus ofclaim 1, wherein the radiation peak intensity detection apparatus islocated in a position where radiation emitted by any one element isincident upon the radiation peak intensity detection apparatus.
 6. Theapparatus of claim 5, wherein the radiation peak intensity detectionapparatus is moveable into and out of the position.
 7. The apparatus ofclaim 1, wherein the radiation peak intensity detection apparatus ismoveable between positions which are adjacent to the elements of theindividually controllable elements.
 8. The apparatus of claim 7, whereinthe radiation peak intensity detection apparatus is moveable betweenpositions which are adjacent to the elements, such that the radiationpeak intensity detection apparatus can be moved to a position where theemission spectrum of a specific individually controllable element can bedetected.
 9. The apparatus of claim 1, wherein the radiation peakintensity detection apparatus comprises: one or more radiation intensitydetectors; and wherein each radiation detector is associated with afilter that is located in a position whereby radiation emitted by anindividually controllable element of the radiation source passes throughthe filter before being detected by the radiation intensity detector.10. The apparatus of claim 9, wherein the radiation peak intensitydetection apparatus comprises: an odd number of radiation intensitydetectors; and wherein each radiation detector is associated with afilter that is located in a position whereby radiation emitted by anindividually controllable element of the radiation source passes throughthe filter before being detected by the radiation intensity detector.11. The apparatus of claim 9, wherein each filter has a differentcentral pass-frequency or pass-wavelength.
 12. The apparatus of claim 9,wherein one filter has a central pass-frequency or pass-wavelength whichcorresponds to a desired frequency or wavelength.
 13. The apparatus ofclaim 1, further comprising a control module configured to control theindividually controllable elements of the radiation source.
 14. Theapparatus of claim 13, wherein the control module: forms a part of theradiation source; or forms a part of the radiation peak intensitydetection apparatus; or is an independent part of the lithographicapparatus.
 15. The apparatus of claim 13, wherein the control module isarranged to control a property that is used to control each of theindividually controllable elements.
 16. The apparatus of claim 15,wherein the control module is arranged to vary a property that is usedto control the individually controllable elements.
 17. The apparatus ofclaim 15, wherein the control module is arranged to control a propertythat is used to control the individually controllable elements, theproperty being a specific property which ensures that an individuallycontrollable element being controlled has a desired peak in its emissionspectrum.
 18. The apparatus of claim 17, wherein the control module isarranged to determine the specific property, or is provided withinformation related to the specific property.
 19. The apparatus of claim15, wherein the property is a current provided to each individuallycontrollable element.
 20. The apparatus of claim 1, wherein the opticalelements are configured to change an emission profile of the associatedindividually controllable element.
 21. The apparatus of claim 20,wherein the plurality of optical elements are diffractive, reflective orrefractive.
 22. The apparatus of claim 1, wherein the individuallycontrollable elements are LEDs or laser diodes.
 23. A lithographicapparatus according to claim 1 wherein individual radiation elements areorganized into an array of individually controllable elements.
 24. Theapparatus of claim 23, wherein the radiation peak intensity detectionapparatus is configured to move between positions which are adjacent tothe array of individually controllable elements.
 25. The apparatus ofclaim 24, wherein the radiation peak intensity detection apparatus isconfigured to move between positions which are adjacent to the array ofindividually controllable elements, such that the radiation peakintensity detection apparatus is moved to a position where the emissionspectrum of a specific individually controllable element is detected.26. The apparatus of claim 23, further comprising a control moduleconfigured to control the array of individually controllable elements ofthe radiation source.
 27. The apparatus of claim 23, wherein the opticalelements are configured to change an emission profile of the associatedindividually controllable element in the array.
 28. A method ofdetecting properties of a radiation source that is used in connectionwith a lithographic apparatus, or provided in the lithographicapparatus, the radiation source comprising an array of individuallycontrollable elements, each individually controllable element beingcapable of emitting radiation, the method comprising: varying a propertythat is used to control an individually controllable element; changingan emission profile of the individually controllable element via atleast two corresponding optical elements, the corresponding opticalelements being provided on a substantially transparent casing integratedwith and surrounding the associated individually controllable element;detecting the intensity of radiation emitted by the individuallycontrollable element as the property is varied in order to identifychanges in the intensity of an emission spectrum of the individuallycontrollable element as the property is varied; and determining aspecific property for which the peak in the intensity of an emissionspectrum of the element is a desired peak.
 29. The method of claim 28,further comprising controlling the individually controllable elementusing the specific property.
 30. The method of claim 29, wherein theindividually controllable element is controlled using the specificproperty during the exposure of a target portion of a substrate.
 31. Themethod of claim 28, comprising repeating the method for a plurality ofindividually controllable elements of the array, or for all individuallycontrollable elements of the array.
 32. The method of claim 28, wherein,before detecting radiation emitted by the individually controllableelement as the property is varied, the method comprises moving adetector into a position where radiation emitted by the individuallycontrollable element can be detected so that the detection may beundertaken.
 33. The method of claim 28, wherein the desired peak is whenthe intensity of the emission spectrum is highest at a desiredwavelength or frequency.